Thermoelectric power plants, including hydrocarbon-fired power plants, such as coal, oil, and/or natural gas-fired power plants, and nuclear power plants, and other heavy industrial processes use very large amounts of water for performing various processes and for providing ancillary function. Often, the water is withdrawn from the surrounding environment, such as a nearby stream or lake, and the water is eventually returned to the stream or lake.
A problem is that the water often becomes contaminated with chemicals and/or other waste products from the industrial process, thereby forming wastewater. It is, therefore, often necessary to process this wastewater to remove some or all of the contaminants prior to returning the wastewater to the environment.
One particular source of wastewater often generated in a hydrocarbon-fired thermoelectric power plant is flue gas desulfurization (“FGD”) purge water, or “blowdown”. FGD purge water is a wastewater or slurry containing sulfur and/or other chemicals removed from a stream of flue gases, i.e., exhaust gases from a boiler or other hydrocarbon-fuel combustion process. FGD purge water is a byproduct of a flue gas desulfurization system, in which sulfur and other contaminants are removed from a flow of flue gases, usually in a component called an absorber. In the absorber, sulfur and/or other contaminants are removed from the flue gases, usually by spraying a stream of flue gases with a water-based slurry carrying various chemicals designed to help remove the sulfur and/or other contaminants from the gases. The slurry is collected after being sprayed into the stream of flue gas and typically is recycled many times through the absorber. FGD purge water is a wastewater stream that is drawn off of the slurry as the buildup of sulfur and/or other contaminants in the slurry increases, for example, to maintain the total dissolved solids (“TDS”) in the slurry within some preselected range or under some preselected upper limit.
Another source of wastewater often generated in electrical power plants and other industrial plants is cooling tower purge water, or “blowdown.” Similar to the FGD purge water, cooling tower purge water is wastewater containing dissolved solids that is drawn off of a supply of water used for cooling exhaust gases, usually to maintain the TDS in the cooling water within or under some preselected range or limits.
A further source of wastewater often generated in power plants is service water, which is used to cool various heat exchangers or coolers in the power house or elsewhere, other than the main condenser. As with the FGD purge water and the cooling tower purge water, the service water usually accumulates dissolved solids, the levels of which usually need to be controlled.
The service water, FGD purge water, and cooling tower purge water usually need to be treated to remove some or all of the dissolved solids before being returned to the environment or recycled for further use within the industrial plant.